In the manufacture of electronic devices, such as liquid crystal displays, where multiple layers of patterned materials are combined to form the display, precise registration of the layers is critical for proper function and acceptable performance.
A liquid crystal display (LCD) is a type of flat panel display used in various electronic devices. At a minimum, an LCD comprises a support, such as glass or plastic, at least one conductive layer and a liquid crystal layer. LCDs may also be more complex and have additional components. For example, an LCD may comprise a transparent, multilayer flexible support, coated with a first patterned conductive layer and coated with a light-modulating liquid crystal layer. A second conductive layer is applied and overcoated with a dielectric layer to which dielectric conductive row contacts are attached, including via holes that permit interconnection between conductive layers and the dielectric conductive row contacts. Other optional functional layers may be applied between the various layers.
The manufacture of display articles in a roll-to-roll fashion is of great interest for the purpose of providing low cost and flexible displays. U.S. Pat. No. 6,394,870 describes a liquid crystal display comprising a cholesteric liquid crystal layer disposed on a patterned conductive layer on a flexible support, with a second conductor that is screen printed in a pattern over the liquid crystal layer. Screen printed dielectric materials with via holes and additional conductive materials are further described. Precise alignment of the patterned second conductor over the first patterned conductive layer in the screen printing operation, precise alignment of the via holes in the screen printed dielectric layer over the second conductor, and precise alignment of the conductive traces over the via holes are all critical steps for the proper function of the display.
An attractive option during manufacture of liquid crystal displays is to screen or ink jet print conductive material as pads for interconnections to the drive electronics directly on the patterned first conductor on the flexible support in an area not covered with liquid crystal or other coatings. In this case, precise alignment of the printed pad to the patterned first conductor is a critical step if the width of the pad approaches the width of the patterned first conductor segment.
U.S. Pat. Application 2004/0048173 discloses a method of aligning a substrate or support for use in manufacture of organic light emitting (OLED) displays with a laser which produces a beam that causes the transfer of organic material from a donor element to the substrate, including providing at least one fiducial mark on the substrate; positioning the substrate relative to the laser and providing relative movement between the substrate and the laser and the laser beam until the laser beam impinges upon the fiducial mark; and detecting when the laser beam impinges upon the fiducial mark and determining the position and orientation of the substrate. The method disclosed in U.S. Pat. Application 2004/0048173 requires that the fiducial mark be present prior to laser deposition and the laser is part of a system to detect the fiducial and to position the subsequent deposition pattern by the laser to the determined position. This differs significantly in that the fiducial pre-exists and should be aligned with some associated alignment error the magnitude of which is a function of the precision of the alignment system but cannot be completely avoided. In the case of the invention disclosed herein, the fiducial is etched by the laser as part of the etch pattern eliminating the alignment error between the fiducial and the pattern.
U.S. Pat. No. 6,668,449 discloses a novel design for a fiducial and pin one indicator that utilizes a single solder resist opening in a die mounting support to perform the combined functions of prior art fiducials and pin one indicators. Methods of fabricating a carrier substrate and fabricating a semiconductor device package using the combination pin one indicator and alignment fiducial of the present invention are also provided. Preferably, the pin one indicator/alignment fiducial is placed adjacent a corner area of a ball grid array, and comprises an “L”-shaped narrow opening in a solder mask layer in which two lines, mutually perpendicular to one another, form components of an X-Y axis. The pin one indicator/alignment fiducial of the present invention is configured to provide only a minimal opening in the solder resist, making smaller pitches between solder balls and tighter dimensional controls possible. Therefore, the present invention is particularly useful for packages in which the solder resist surface of the mounting substrate is heavily populated with solder ball contact pads and/or and solder balls, and/or in applications where the chip outline is nearly the same size as the package (e.g., Chip Scale Packages (CSP), Near Chip Size (NCS), etc This invention differs significantly, in that the single solder resist opening pertains to die mounting. Further, the fiducial is an opening in the solder resist on a die mounting support, instead of etched areas of ITO and flexible substrate. Still further, the etched fiducial in the ITO is detected and used for alignment. Detection is difficult except for the dark field and incident light methodology.
U.S. Pat. No. 6,236,442 discloses a display and a method of making a display for presenting selected images to a viewer, including a transparent substrate; a transparent, electrically conductive coating formed over the transparent substrate; a light modulating layer formed over the transparent, electrically conductive layer; and a patterned conductive layer formed over the light modulating layer which provides viewable and conductive images, the light modulating layer being effective in two conditions, in a first condition to prevent the viewing of the viewable and conductive images and in a second condition to permit the viewing of the viewable and conductive images. The display is formed by providing a transparent substrate; forming a transparent, electrically conductive coating over the transparent substrate; forming a light modulating layer including liquid crystal material in a polymer binder over the transparent, electrically conductive layer; forming a metallic conductive layer directly on the light modulating layer and removing selected portions of the metallic conductive layer to provide viewable and conductive images, and providing electrical connection so that an electrical field can be applied across selected ones of such viewable and conductive images and the transparent, electrically conductive layer to cause the light modulating layer underlying the selected ones of the viewable and conductive images to change from the first condition to the second condition so as to present such viewable and conductive images for viewing to the viewer.
Application of the current art of a printed ink or stamped out hole serving as an alignment feature created on the flexible support prior to the patterning of the first conductive layer complicates the patterning process as the pattern should be positioned relative to the alignment feature. The magnitude of the resulting alignment error is a function of the sophistication of the patterning equipment. However large or small, the error propagates through all future alignment steps increasing the overall error. In order to avoid this error, the alignment feature should be created in the transparent conductive support during the patterning step, however there is still a need for reading the nearly transparent alignment indicia.